Semiconductor processing involves a number of different chemical and physical processes whereby minute integrated circuits are created on a substrate. The integrated circuits are constructed using multilayers of interrelated patterns of various materials, the layers being created by such processes as chemical vapor deposition (CVD), physical vapor deposition (PVD), and epitaxial growth. Some layers are patterned using photoresist masks and wet and dry etching techniques. Patterns are created within layers by the implantation of dopants at particular locations. The substrate upon which the integrated circuit is created may be silicon, gallium arsenide, glass, or other appropriate material.
Many of the processes carried out within semiconductor processing systems leave contaminant deposits on the walls of the process reactor chamber which accumulate and become the source of particulate matter harmful to the creation of a semiconductor device. As the geometries of semiconductor devices become ever so smaller, the ability to maintain the uniformity and accuracy of critical dimensions becomes strained. In this dimensional downsizing environment, the avoidance of contaminant particulate matter upon the surface of the semiconductor workpiece has become more critical.
In addition to the problem of workpiece contamination presented by the process generation and deposition of particulate contaminants on the semiconductor chamber wall, those contaminant particles escaping the chamber through the vacuum conductance system tend to deposit and accumulate on the inner walls of the vacuum conduit channel between the chamber and vacuum pump. The build-up of these particulate deposits will inevitably reduce or clog the vacuum flow conductance from the chamber and increase the speed of the pump to attempt maintenance of the minimum pressure of the chamber. And further, the buildup on the valves in the conduit channel cause their manipulative shut-off function to be negatively affected to a point where their use in regulating vacuum in the chamber is unpredictable and ineffective. To avoid problemsome residue accumulation in the vacuum system, regular and frequent cleaning of the vacuum conduit system would be necessary.
Particulate contamination buildup on semiconductor process chamber walls and vacuum conduit channels is particularly significant in the etch processing of semiconductor elements employing metal films. These metal films are generally etched by employing a number of reactive gases, including halocarbon gases, as plasma components. In the case of an aluminum film, the etchant gases used are predominantly the chlorine containing gases, chlorine (Cl.sub.2) and boron trichloride (BCl.sub.3), which enables formation of volatile aluminum chloride compounds upon etching, which volatile compounds can be removed from the etch processing chamber by applied vacuum. However, simultaneously with the formation of volatile aluminum chloride compounds, other active chlorine and boron containing species are formed which can react with any oxygen and water vapor present in the etch processing chamber or with organic species from patterning photoresist to form non volatile particulate compositions which ultimately produce relatively large quantities of contaminant on the inner walls of the process chamber. The non volatile particulate compositions initially tend to remain inside the etch chamber in the form of loosely attached particles to the chamber etch surfaces. These loosely attached etch by-product compounds can easily break free of the surface to which they are attached and fall upon a workpiece/substrate surface causing contamination of the workpiece surface, thereby resulting in a defective device. And, as indicated above, the build-up of etch contaminant on the vacuum conduit system will result in the diminished function or clogging of the vacuum source. As in the case of any semiconductor process system, the chamber and vacuum exhaust exits of the apparatus employed in metal etch must be cleaned periodically in order to avoid these problems and, of course, such cleaning requires shutdown of the plasma operation with consequent loss of production.
Known plasma chamber cleaning methods have involved opening the plasma etch chamber, disassembling portions of the chamber, and removing the contaminant deposits by physical of chemical methods. For example, the chamber can be rinsed with a solution of hydrochloric acid, or hand wiped with a solvent, to dissolve various contaminants. The etch chamber alternatively may be washed with water and dried. The same cleaning techniques are separately applied to the vacuum conductance channels and pump system to avoid the inevitable diminished vacuum or suffocation referred to above. All of these cleaning methods are complicated, disruptive, time consuming and can be sources of additional contamination.
Plasma enhanced dry cleaning processes exist whereby contaminants attached to the inside walls of a film deposition reaction chamber are removed by plasma etching using carbon tetrachloride and oxygen. However, presently known plasma enhanced dry cleaning systems require a dry cleaning time period equal to about 5% to 10% of the time spent in the aluminum etching process itself. Moreover, the dry cleaning plasma processes are generally ineffective with respect to the vacuum exhaust system which would have to be separately cleaned. It would clearly be advantageous to delay cleaning of plasma etch process chambers and the present invention effects such a result by providing the chamber and vacuum exhaust systems with a coating of a halogenated polymeric material having certain characteristics.
U.S. Pat. No. 5,087,727 to R. J. Steger, issued Feb. 4, 1992, discloses an improved plasma etching apparatus comprising an etch chamber having inner metal surfaces coated with a conductive coating capable of protecting such inner metal surfaces from chemical attack by reactant gases such as halogen-containing gases used in the chamber during the plasma etching process. In a preferred embodiment, a carbon coating having a thickness of at least about 0.2 micrometers is formed on the inner metal surfaces of the etch chamber by a plasma assisted CVD process using a gaseous source of carbon and either hydrogen or nitrogen or both.
U.S. Pat. No. 4,372,807 to Vossen et al., issued Feb. 8, 1983, discloses a process of plasma etching of aluminum in which the hydrocarbon gases, cyclopropane and ethylene, are added to the etchant gases and polymerized on the sidewalls of the etched aluminum to effect sidewall passivation thereby reducing undercutting and improving etch uniformity. The patent is silent as to any deposition of hydrocarbon polymer, or contaminant build-up, on the reactor walls.
U.S. Pat. No. 4,786,359 to Stark et al., issued Nov. 22, 1988, describes a plasma. etch process and apparatus in which silicon wafers are etched using a plasma assisted gas mixture comprising CF.sub.3 Br and xenon or krypton. The patent teaches that the use of this halocarbon etchant gas results in polymer film deposition in the plasma reactor and cites such formation as a negative factor in the plasma etching process because of changes in the electrical characteristics of the reactor chamber and the presence of the polymer deposit as a source of particle contamination for the target wafer. The patent describes a means of preventing or eliminating buildup of the polymer by the use of oxygen in the etchant gas mixture and a sacrificial graphite ring.
All of the cited prior art describe the polymerization of an organic material under glow discharge conditions and deposition of a coating of polymer on the metallic sidewall of a workpiece and/or the plasma chamber walls. In one case, it is desired to deposit such a coating, which is used to aid device fabrication by assisting in the prevention of metal sidewall undercutting. In another case, a coating was intentionally deposited on the plasma etch chamber wall to protect the wall from corrosion by active species created during plasma glow processing. In still other cases, the polymer build up on etch chamber walls is a contaminant which must be periodically removed to prevent particulate flaking and device contamination.
In copending application to Shamouilian et al., Ser. No. 08/138,518, filed Oct. 15, 1993, and now abandoned, there is described a means of preventing the particulate flaking of plasma etch by-product buildup generated during metal etch processing, wherein organic materials are polymerized under glow discharge conditions and deposited as a coating on the contaminant laden surface of the chamber walls. The polymer coating entraps the contaminants and provides a fresh wall surface thereby extending the productive use time of the plasma processing chamber without the need for time consuming cleaning. However, even in the case of this improved contaminant control development, the layer of entrapped contaminants must be cleaned off the plasma processing chamber walls more frequently than contemplated with the use of the instant halogenated polymeric coatings.
It would be desirable to have a semiconductor processing apparatus and method of operation which prevents sticking or accommodation of semiconductor process residue build-up on the surface of the reactor chamber walls or the vacuum conduit channel means communicating with the chamber.